The present invention relates to a pressure core barrel assembly for recovering a core at formation pressure and is specifically directed to improvements in the type of pressure core barrel described in U.S. Pat. No. 3,548,958 issued 12/27/70 to Blackwell and Rumble. In such a pressure core barrel assembly it is important to know that the pressure core barrel has been sealed at formation pressure before the barrel is raised to the surface. If it is not sealed the sample will not be representative of the actual conditions existing in the formation at the bottom of the well.
Present practice requires that the core be frozen under pressure to trap the fluids in the core so that removing the pressure will not alter fluid content of the core.
In order to be able to disassemble the barrel and remove the frozen core for analysis, the drilling mud, containing fluid and cuttings, in the barrel must be displaced with a fluid such as gelled kerosene which will not freeze at dry ice temperatures.
Prior art core barrels including the one disclosed in U.S. Pat. No. 3,548,958 are equipped with internal ports and valves so that this displacement or flushing can be done while pressure is maintained on the core. These internal valves are a frequent cause of leakage and loss of pressure. Additionally, because of space limitations the internal ports are small and frequently clog with drilling mud or cuttings during flushing. This results in only partial flushing and subsequent freezing of the mud between the inner and outer barrel and around the ball valve assembly. The ball valve must also remain closed during flushing and freezing. The ball valve and operator are frequently frozen to the core barrel because of insufficient flushing in this area of the tool. This often results in damage to the ball valve operator and gears when the ball valve is opened after freezing to remove the core.